/Engine/Source/Runtime/Core/Public/Misc/StringBuilder.h
This function is only available when the elements of the range and the delimiter can both be written to the builder using the append operator.
The builder, to allow additional operations to be composed with this one.
template<typename RangeType, typename DelimiterType, std::enable_if_t< TCanAppendRange_V< RangeType && > &&TCanAppend_V< DelimiterType && >> *> [BuilderType](API\Runtime\Core\Containers\TStringBuilderBase\BuilderType) & Join ( RangeType && InRange, DelimiterType && InDelimiter )